During the perioperative period, the anesthetist has to monitor, control and interpret a great number of factors having an influence on the patient's well being. These factors are, in particular, hemostasis, oxygenation, nutrition, ph-level and body temperature. Further, the anesthetist must evaluate the influence of a blood product being transfused to a patient who has suffered a severe loss of blood.
Hemostasis is the process by which bleeding from a damaged blood vessel stops. It is a dynamic, extremely complex process involving many interacting factors, which include coagulation, i.e. the process by which blood clots are formed, fibrinolytic proteins, activators, inhibitors and cellular elements. Since none of these factors remains static or works in isolation, it is necessary to measure continuously all phases of a patient's hemostasis as a net product of all blood components in a non-isolated and non-static fashion.
Furthermore, it is well known that coagulopathy is sometimes confused with hypothermia, acidosis and preexisting disorders like morbid ionized calcium concentration. For example:                Trauma patients are prone to hypothermia, which slows down enzymatic reactions, modifies platelet function, decreases platelet counts and stimulates fibrinolysis.        Acidosis worsens fibrin polymerization and strengthening of the clot.        Low ionizied calcium concentration (as the result of a massive PRBC transfusions containing citrate) and a low hematocrit (<30%) further aggravate bleeding diathesis.        Increased base deficit (BD) or decreased base excess (BE), respectively, are known to influence the haemostatic potential.        
Various methods have been introduced to assess hemostasis parameters like the potential of blood to form an adequate clot. Common laboratory tests such as thrombocyte counts or the determination of fibrin concentration provide information on whether the tested component is available in sufficient amount but lack in answering the question whether the tested component works properly under physiological conditions (e.g. the activity of fibrinogen under physiological conditions cannot be accessed by common optical methods).
A group of tests which overcomes these problems is summarized by the term “viscoelastic methods”. The common feature of these methods is that the blood clot firmness (or other parameters dependent thereon) is continuously determined, from the formation of the first fibrin fibres until the dissolution of the blood clot by fibrinolysis. Blood clot firmness is a functional parameter, which is important for hemostasis in vivo, as a clot must resist blood pressure and shear stress at the site of vascular injury. Clot firmness results from multiple interlinked processes: coagulation activation, thrombin formation, fibrin formation and polymerization, platelet activation and fibrin-platelet interaction and can be compromised by fibrinolysis. Thus, by the use of viscoelastic monitoring all these mechanisms of the coagulation system can be assessed.
The first viscoelastic method was called “thromboelastography” (Hartert H: Blutgerinnungsstudien mit der Thromboelastographie, einem neuen Untersuchungsverfahren. Klin Wochenschrift 26:577-583, 1948). In the thromboelastography, the sample is placed in a cup that is periodically rotated to the left and to the right by about 5°, respectively. A pin is freely suspended by a torsion wire. When a clot is formed it starts to transfer the movement of the cup to the pin against the reverse momentum of the torsion wire. The movement of the pin as a measure for the clot firmness is continuously recorded and plotted against time. For historical reasons the firmness is measured in millimeters.
One of the most important parameters determined by thromboelastography is the time between the activator induced start of the coagulation cascade and the time until the first long fibrin fibres have been built up which is indicated by the firmness signal exceeding a defined value. This parameter will be called clotting time in the following. Another important parameter is the clot formation time which gives a measure for the velocity of the development of a clot. The clot formation time is defined as the time it takes for the clot firmness to increase from 2 to 20 mm. The maximum firmness a clot reaches during a measurement, further on referred to as maximum clot firmness or just MCF, is also of great diagnostic importance.
Modifications of the original thromboelastography technique (Hartert et al. (U.S. Pat. No. 3,714,815) have been described by Cavallari et al. (U.S. Pat. No. 4,193,293), by Do et al. (U.S. Pat. No. 4,148,216), by Cohen (U.S. Pat. No. 6,537,819), further modifications by Calatzis et al. (U.S. Pat. No. 5,777,215) are called thromboelastometry.
Besides hemostasis, parameters like oxygenation, nutrition and ph-level need to be analyzed by the anesthetist. It is commonly known to use blood gas analyzers as described in EP 1 367 392 A1 for this purpose. Blood gas analyzers generally measure the partial pressures of certain gases in a blood sample and other parameters like ph-level and hematocrit. From these partial pressures oxygenation and other factors can be deduced. Devices known as clinical chemistry analyzers are also available in the market. These devices are also used to determine some of the parameters determined by blood gas analyzers. When it is referred to blood gas analyzers henceforth, this is also to include clinical chemistry analyzers and electrolyte analyzers. Further, when it is referred to blood gas parameters henceforth, this is also to include clinical chemistry parameters and electrolyte parameters.
Further, in current practice blood products are usually prepared and applied according to fixed protocols independently from any individual properties of the initial donor or other influences (e.g., storage duration, storage conditions, etc.). In particular, their potential to interact with other factors like the patient's oxygenation, ph-level or hemostasis are not assessed prior to application of the blood products nowadays.
Monitoring, controlling and interpreting this great number of factors as well as their interdependence, especially in stressful environments like operation theaters, put great pressure on the anesthetist. This pressure may result in mistakes with severe consequences for the patient.
It is therefore an object of the present invention to support the anesthetist and/or provide the anesthetist with information in a better way.